A mouse or a track ball is an input device for controlling the motion of a cursor on a monitor. A mouse controller is a device installed in a mouse for executing the cursor-control function of the mouse. A similar device can be applied to a track ball for executing the cursor-control function of the track ball.
Please refer to FIG. 1 which is a schematic circuit diagram showing a mouse including a first kind of conventional mouse controller. The mouse shown in FIG. 1 includes a photo coupler 1 composed of a light-emitting diode 11 and a photo diode 12, a mouse controller 2 composed of a constant resistor R21, a reference voltage supplier Vref, a comparator 22 and a shift controller 23, and a limited current resistor R1. When the ball of the mouse (not shown) drives a grid wheel of the mouse (not shown), the light-emitting diode 11 provides a light source emitting through the holes spacedly arranged on the grid wheel to be intermittently received by the photo diode 12. The photo diode 12 generates an induced current in response to the quantum of the received light. The constant resistor R21 causes the output terminal A of the photo coupler 1 to output a voltage in response to the induced current. The comparator 22 compares the value of the voltage at the location A with that of the reference voltage generated by the reference voltage supplier Vref to obtain a digital state (0,1) state, thereby detecting the rotation situation of the grid wheel. The shift controller 23 receives the digital state to control the motion of the cursor on the monitor.
Owing to the transient capacitor effect, when the voltage value at A increases, a value of the voltage in response to the maximal induced current is reached at the input terminal In1 of the comparator 22 after a period of capacitor charging time. That result in an accurate input voltage value obtained by the comparator 22 for being compared with the reference voltage. A more precise result is thus able to be obtained. On the contrary, when the induced current declines, a period of discharging time is also required for achieving a more accurate comparison. However, because resistor R21 is a constant resistor, the resistance thereof cannot vary with the voltage value at A. In other words, the charging and/or discharging time R.times.C (resistance times capacitance) of the photo diode 12 cannot be shortened. If the changing rate of the light-shield/light-pass state through the grid wheel is too high, an erroneous comparing result will possibly be generated by the comparator 22 so that the frequency response of this kind of conventional mouse controller is unsatisfactory. In addition, the light-leakage phenomenon occurred in the photo coupler 1 often influences the operation result of the comparator 22. Therefore, this kind of mouse controller is suitable only for applications in which high resolution is not required.
Please refer to FIG. 2 which is a schematic circuit diagram showing a mouse including a second kind of conventional mouse controller. In FIG. 2, a photo coupler 3 and a mouse controller 4 are shown. The photo coupler 3 includes a light-emitting diode 31 and a photo diode 32. The mouse controller 4 includes a constant resistor R411, dynamic resistor means M412 being a MOS transistor, a comparator 42, a reference voltage supplier Vref, and a shift controller 43. The circuit diagram shown in FIG. 2 includes all the circuit shown in FIG. 1 and the identical portions of the circuits in both figures perform the same function. The difference between the first and the second kinds of conventional mouse controllers lies in that the second one includes the dynamic resistor means M412 which is absent in the first one. The dynamic resistor means M412 is a MOS transistor. As what is known to those skilled in the art, the impedance of a MOS transistor will decrease with the increase of the input voltage after the MOS transistor is conducted. Therefore, when the voltage value at B increases, the impedance of the dynamic resistor means M412 will decrease to shorten the charging time R.times.C of the photo diode 32. The aforementioned result is supported by the reason that the resistor R411 and the dynamic resistor means M412 are connected in parallel. When the impedance of the dynamic resistor means M412 decreases, the equivalent resistance R decreases, too, and thus the charging time R.times.C is shortened. This kind of conventional mouse controller has a better frequency response and can overcome the light-leakage phenomenon which occurs in the photo coupler 3, thereby obtaining a higher resolution.
Unfortunately, there are still problems encountered in the detection and comparison operations of this kind of mouse controller 4. In general, the reduction of the charging time will assure a good detection in the light-pass state through the grid wheel. The reduction of the discharging time is also preferably required in the light-shield state through the grid wheel. Shorter charging/discharging time will cause clear high/low pulses to be produced to obtain accurate detection. On the contrary, improper charging/discharging time will render the waveforms of two cycles to overlap. Although, under a light-pass state where a relatively higher voltage at B is caused by the light passing through the grid wheel and received via the photo diode, the dynamic resistor means M412 enables the comparator 42 to operate. However, under a light-shield state, the dynamic resistor means M412 cannot discharge promptly the charges at B, and therefore, the detection and comparison operation of the comparator 42 are adversely influenced.
The reference voltage supplier Vref shown in FIG. 1 or 2 is illustrated as follows with reference to FIG. 3. As shown in FIG. 3, the reference voltage supplier Vref includes two voltage-dividing resistors Rd1 and Rd2. The voltage value supplied from this kind of reference voltage supplier Vref is subject to variation in response to the change of the work voltage V.sub.DD, and thus the operation result of the comparator is possibly erroneous.
An object of the present invention is to provide an input device controller using multi-stage dynamic impedances for an impedance match to obtain better frequency response and accurate identification of light-pass/light-shield state.
Another object of the present invention is to provide an input device controller using a reference voltage supplier including a constant current generator and an equivalent circuit to avoid the bad effect on the cursor shift control, caused by the variation of the reference voltage.
In accordance with the present invention, an input device controller to be used with an input device having a photo coupler generating an induced current in response to a received quantum of light includes a first resistor means electrically connected to the photo coupler in order that the photo coupler has an output voltage in response to the induced current, a second resistor means electrically connected to the photo coupler and having the resistance thereof varying with the output voltage for preventing the photo coupler from being overcharged, and a controlling means electrically connected to the photo coupler for controlling a cursor on a monitor in response to the output voltage.
The controlling means includes a reference voltage supply circuit for supplying a reference voltage, a comparator having a first input terminal electrically connected to the photo coupler and a second input terminal electrically connected to the reference voltage supply circuit for comparing the output voltage and the reference voltage to output a digital signal, and a shift controller electrically connected to the comparator for controlling a movement of the cursor on the monitor in response to the digital signal.
The first resistor means is a constant resistor. The second resistor means is a dynamic resistor means preferably including a plurality of metal-oxide-semiconductor field-effect transistors (MOSEFTs) and a Bipolar Junction Tranisitor (BJT). The dynamic resistor has an impedance which decreases with the increase of the output voltage of the photo coupler. The present input device controller preferably further includes a third resistor means electrically connected between the first and the second resistor means and having the resistance thereof vary with the output voltage of the photo coupler. The third resistor means is a dynamic resistor means preferably including a MOSFET and the impedance thereof decreases with the increase of the output voltage of the photo coupler. The maximum value of the impedance of the third resistor means is smaller than that of the first resistor means but greater than that of the second resistor means.
The reference voltage supply circuit preferably includes a constant current generator for generating a constant current, and a dynamic impedance-input circuit electrically connected between the constant current generator and the second input terminal of the comparator, and including a constant input resistor performing the same function as the first resistor means and a first dynamic input resistor performing the same function as the third resistor means so that the comparator is able to compare the output voltage of the photo coupler with the reference voltage by comparing the induced current generated by the photo diode with the constant current generated by the constant current generator. A value of the constant current generated by the constant current generator is within a current range measured at the first input terminal of the comparator when the second resistor means is conducted.
The constant current generator preferably includes a voltage-dividing resistor means including two resistors, a voltage-dividing comparator, one input terminal of which is electrically connected between the two resistors of the voltage-dividing resistor means, a MOSFET, the gate of which is electrically connected to an output terminal of the voltage-dividing comparator, a current-adjusting resistor electrically connected to another input end of the voltage-dividing comparator and the source of the MOSFET for adjusting the constant current, and a current mirror electrically connected between a drain of the MOSFET and the dynamic impedance-input circuit. On the other hand, the dynamic impedance-input circuit preferably further includes a second dynamic input resistor performing the same function as the second resistor means, and electrically connected between the first dynamic input resistor and the second input terminal of the comparator.
In accordance with another aspect of the present invention, an input device controller to be used with an input device having a photo coupler generating an induced current in response to a received quantum of light comprising a first resistor means electrically connected to the photo coupler in order that the photo coupler has an output voltage in response to the induced current, a second resistor means electrically connected to the photo coupler and having the resistance thereof varying with the output voltage, a constant current generator for generating a constant current, a dynamic impedance-input circuit electrically connected to the constant current generator and including a first input resistor having a resistance characteristic identical to that of the first resistor means and a second input resistor performing the same function as the second resistor means, and a controlling means electrically connected to the photo coupler and the constant current generator for controlling a movement of a cursor on a monitor in response to a compared result of the induced current and the constant current.
Each of the first resistor means and the first input resistor is a constant resistor, and each of the second resistor means and the second input resistor is a dynamic resistor means including a MOSFET and having an impedance which decreases with an increase of the output voltage of the photo coupler.
The controlling means includes a comparator having a first input terminal electrically connected to the photo coupler and a second input terminal electrically connected to the constant current generator for comparing the induced current and the constant current to output a digital signal, and a shift controller electrically connected to the comparator for controlling the movement of the cursor on the monitor in response to the digital signal. A value of the constant current generated by the constant current generator is within a current range measured at the first input terminal of the comparator if the second resistor means is not conducted.
The present input device controller preferably further includes a third resistor means electrically connected to the photo coupler and having the resistance thereof varying with the output voltage, and the dynamic impedance-input circuit further including a third input resistor electrically connected between the first input resistor and the second input terminal of the comparator and performing the same function as the third resistor means. Each of the third resistor means and the third input resistor is a dynamic resistor means including a plurality of MOSFETs and a BJT, and the impedance of the dynamic resistor means decrease with the increase of the output voltage of the photo coupler. The maximum of the impedance of the second resistor means is smaller than that of the first resistor means but greater than that of the third resistor means. In this situation, a value of the constant current generated by the constant current generator is within a current range measured at the first input terminal of the comparator when the third resistor means is conducted.
The constant current generator preferably includes a voltage-dividing resistor means including two resistors, a voltage-dividing comparator, one input terminal of which is electrically connected between the two resistors of the voltage-dividing resistor means, a MOSFET, the gate of which is electrically connected to an output terminal of the voltage-dividing comparator, a current-adjusting resistor electrically connected to another input end of the voltage-dividing comparator and the source of the MOSFET for adjusting the constant current, and a current mirror electrically connected between a drain of the MOSFET and the dynamic impedance-input circuit.
The present input device controller is preferably used for an input device such as a mouse.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: